1. Technical Field of the Invention
This invention relates to electrical contacts and, more particularly, to apparatus and a method for affixing bondable finger contacts to printed circuit boards.
2. Description of the Prior Art
A conventional method for electrically connecting plug-in printed circuit boards to mating backplane connectors utilizes patterned and plated fingers at the board edge. These fingers are usually an extension of the circuit pattern. They are plated with a sequence of metallization layers to provide low contact resistance between the mating parts of the connector over the circuit life.
Another method for providing finger contacts on printed circuit boards is disclosed in H. E. Spooner et al U.S. Pat. No. 3,396,461, issued Aug. 13, 1968. In Spooner et al the contact elements are carried on a common support strip. The strip is positioned over the conductor patterns on the circuit board thereby bringing the contact elements into alignment with the conductor patterns. The contact elements are then bonded to the conductor patterns by welding or soldering after which the common support strip is removed.
Still another method for terminating printed circuit boards utilizes a double-sided piece of adhesive tape to fasten a connector along the edge of the board. This approach to board termination is disclosed in R. D. Nelson U.S. Pat. No. 3,704,515 issued Dec. 5, 1972. In Nelson the connector contacts are bent at right angles to facilitate engagements with apertures in the printed circuit board. Once the contacts are inserted into the apertures, they are held securely in place by solder.
A somewhat related method for terminating circuit modules is disclosed in C. W. Wallach U.S. Pat. No. 4,044,201, issued Aug. 23, 1977. In Wallach a lead frame assembly includes a pair of spaced-apart, parallel carrier strips with a plurality of collapsible rungs extending between the strips at regular intervals along its length. The rungs are collapsed inwardly to seat against the sides of the circuit module which is positioned between the ends of the leads. After seating, the lead ends are soldered to metallized surfaces on the module. Following bending of the leads, the carrier strips and rungs are cut away.
Apparatus for attaching multiconductor flat cable to an electrical connector is disclosed in W. R. Over et al U.S. Pat. No. 3,938,246, issued Feb. 17, 1976. The apparatus employs a movable ram which moves through multiple strokes to perform all of the necessary steps. A movable connector holder is utilized so that cables may be attached to opposite faces of the connector by using a single, movable ram. The contacts used in effecting this type of termination are manufactured by punching a thin strip of metal to form individual contacts. Plastic carrier strips are applied to opposite edges of the contacts to provide support after the contacts are severed from their metallic support strip.
A number of problems exist in the above methods for mounting prefabricated finger contacts. In particular, for extremely densely patterned printed circuit boards where the spacing between adjacent conductor patterns might be on the order of 62.5 mils, prefabricated fingers have to be retained in relatively precise alignment during attachment. In view of this conductor spacing it is oftentimes necessary to put contact fingers on both sides of the board even though the circuit pattern appears only on one side of the board. None of the aforementioned references addresses these problems. Moreover, in those methods where the carrier support strip is severed following the bonding operation, both the contacts and the board are susceptible to damage along the leading edge. This is especially true where the boards are uneven.
In order to circumvent these problems, we have developed apparatus and a method for affixing bondable finger contacts to a printed circuit board which facilitates increasing the number of available contact positions by mounting finger contacts on both sides of the printed circuit board. By virtue of this approach access is gained to a single-sided circuit from both sides of the printed circuit board along the edge mounted contacts. This solution is attractive because finger contact alignment is controllable during the bonding operation. In addition, the possibility of board and contact damage caused by sharp contact edges is greatly reduced.
Additional benefits to be derived from this approach to solving the above-noted problems are that the contact metal plated areas of the contacts are protected from damage during installation. Furthermore, the finger contacts are mounted in such a way that individual contacts which may become damaged during subsequent handling or use of the printed circuit board may be advantageously individually repaired.